pgsql: Require hostname to be set when using GSSAPI authentication.

Log Message:
-----------
Require hostname to be set when using GSSAPI authentication. Without it,
the GSSAPI libraries crash.

Noted by Zdenek Kotala

Modified Files:
--------------
pgsql/src/interfaces/libpq:
fe-auth.c (r1.143 -> r1.144)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-auth.c?r1=1.143&r2=1.144)